In the state of art, such a strut type suspension is proposed in JP11-48728 A, in which the coil center axis (axis line) of a coil spring is set in a twisted relationship with respect to a kingpin axis so as to generate moment around the kingpin axis in a toe-in direction, in order to improve responsiveness, stability, and straight line in stability of a vehicle.
By the way, in such a strut type suspension as mentioned above, depending on ways to set the twisted relationship between the coil center axis and the kingpin axis, the twisted relationship of the coil center axis with respect to the kingpin axis may change when the upper spring seat of the coil spring rotates at the up-and-down stroke operation of the suspension, resulting in change in moment-arm length. At this time, if winding directions of the coil springs for left and right wheels are set to be the same, a difference in moment-arm length between the suspension on the left side and the suspension on the right side occurs during stroke operations of the left and right suspensions in phase, which causes the generation of a steering moment for both of the left and right wheels in the same direction (e.g. in a right-side steering direction), leading to a problem of vehicle pull.